For a variety of applications, the close control of the thickness of manufactured substrates can be important if not critical. For example, diverse procedures have been implemented and proposed for controlling thickness variations that can occur in liquid crystal display (LCD) glass manufactured by a fusion downdraw method causing variations in the thickness of the glass ribbon. Thermo-mechanical and glass flow conditions can be uneven across the entirety or portions of a width of a glass ribbon as it is being formed in the fusion downdraw method. Typically, the surface tension at the glass ribbon as it is being formed is inadequate to entirely obviate the variations that can occur in the thickness of the glass ribbon. Although the variations may be only a few microns in size, the consequences of such variations can be significant with respect to LCD glass for example. One technique for controlling thickness variations is disclosed in U.S. Pat. No. 8,196,431 to Steven R. Burdette.